example.py

logger = Logger(
    service="my-lambda-service",            # or any service name
    utc=True,
    # Setting formatter_cls doesn't exist directly—pass an instance as below
    logger_formatter=OtelJsonFormatter(),
    # log_level="INFO",  # optionally set a log level
)

otel-powertools-logger.py

import json
import os
import logging
import time
from typing import Any, Dict
from aws_lambda_powertools import Logger
from aws_lambda_powertools.logging.formatter import JsonFormatter

def _map_python_level_to_severity_number(levelno: int) -> int:
    """Map Python's logging level numbers to an approximate OTel severity_number."""
    # Common mapping, can be adjusted
    if levelno <= logging.DEBUG:
        return 5   # TRACE or DEBUG range
    elif levelno <= logging.INFO:
        return 9   # INFO
    elif levelno <= logging.WARNING:
        return 13  # WARN
    elif levelno <= logging.ERROR:
        return 17  # ERROR
    else:
        return 21  # FATAL

class OtelJsonFormatter(JsonFormatter):
    """
    Custom JSON formatter to produce logs that align with OpenTelemetry log data model.
    """

    def format(self, record: logging.LogRecord) -> str:
        # Default attributes from the record
        log_message = record.getMessage()           # main log string
        level_text = record.levelname               # e.g. INFO, DEBUG, ERROR
        level_number = _map_python_level_to_severity_number(record.levelno)
        
        # The timestamp when the record was created, in RFC3339 or epoch
        # record.created is float seconds since epoch. Convert to milliseconds or ISO 8601.
        # For OTel logs, you can use an RFC3339/ISO 8601. We'll do an ISO8601 here.
        timestamp = time.strftime("%Y-%m-%dT%H:%M:%S", time.gmtime(record.created)) \
                    + f".{int((record.created - int(record.created)) * 1_000_000):06d}Z"
        
        # Build the resource block. In a Lambda, you can capture function name, region, etc.
        resource = {
            "cloud.provider": "aws",
            "cloud.platform": "aws_lambda",
            "cloud.region": os.environ.get("AWS_REGION"),
            "faas.name": os.environ.get("AWS_LAMBDA_FUNCTION_NAME"),
            "faas.version": os.environ.get("AWS_LAMBDA_FUNCTION_VERSION"),
        }

        # If you want trace_id/span_id correlation from X-Ray, parse them from environment
        # or from a custom context. This is a simplified example.
        xray_trace_id = os.environ.get("_X_AMZN_TRACE_ID", "")
        # A typical X-Amzn-Trace-Id looks like:
        #  Root=1-6483fcc6-2efd98a76b34c26a6609337e;Parent=1234567890abcdef;Sampled=1
        trace_id = None
        span_id = None
        if "Root=" in xray_trace_id and "Parent=" in xray_trace_id:
            # Extract Root=1-xxxxxx-xxxxxxxxxxx
            root_part = xray_trace_id.split("Root=")[1].split(";")[0]
            # OTel’s 128-bit trace IDs do not match 1-xxxx-xxxx directly,
            # but you can transform them for correlation.  For brevity:
            trace_id = root_part.replace("-", "")
            
            parent_part = xray_trace_id.split("Parent=")[1].split(";")[0]
            span_id = parent_part
        
        # Additional fields you might store as attributes
        # This merges any custom fields from the record's "extra" dictionary
        # (i.e., `logger.info("...", extra={"key": "value"})`)
        attributes: Dict[str, Any] = {}
        if hasattr(record, "extra"):
            attributes.update(record.extra)

        # Construct the OpenTelemetry-like log record
        otel_log = {
            "timestamp": timestamp,
            "severity_text": level_text,
            "severity_number": level_number,
            "body": log_message,
            "attributes": attributes,
            "resource": resource,
        }

        # Add trace info if present
        if trace_id:
            otel_log["trace_id"] = trace_id
        if span_id:
            otel_log["span_id"] = span_id
        
        # Return as a JSON string
        return json.dumps(otel_log, ensure_ascii=False)